The front and rear driving sprockets of bicycles are typically coupled by a chain, which must be provided with the correct tension to function properly. However, it is impractical to manufacture highly precise components for providing the correct tension. In addition, adjustability of the components is highly desirable for installation and maintenance of the chain. It is therefore, well known and conventional to provide for fore and/or aft adjustment of the rotational axis of the front pedal crank spindle, on which the front driving sprocket is mounted. Among the adjusting devices known for this purpose are so-called eccentric mounts, in which the rotary axis of the spindle is eccentric to a cylindrical casing that is rotatable among adjusted positions in a shell. The shell is arranged to hold the casing in the adjusted position.
One arrangement for fixing the eccentric in the adjusted position is to use a split shell and two binder blocks, which tighten the shell to clamp the spindle casing in the adjusted position. This design is similar to the way in which the heights of bicycle seat posts are adjustably changed within the seat tube. Another known arrangement is based on a setscrew concept. However, a major disadvantage of both these designs is that both the binder block and set screw designs involve components external to the shell that detract from the appearance of the assembly, as compared to a conventional bottom bracket assembly, and both require extra manufacturing operations, which increase labor costs, such as the costs of splitting the shell and welding or brazing on fittings.
Another concept is disclosed in U.S. Pat. No. 4,808,147 (“the '147 patent”) in which an eccentrically mounted spindle that is rotatably adjustable in a sleeve was provided having no external elements. This concept solved a number of the problems mentioned in the prior art. However, the bracket taught in the '147 patent comprises a solid body portion having a single planar wedge surface that is designed to co-act with a wedge. Due to the single planar wedge surface, the overall weight of the bracket is increased. In addition, the relatively large surface area of the single planar wedge surface may contribute to sticking of the wedge to the single planar wedge surface when attempting to remove the wedge therefrom.
Therefore what is desired then is a design that reduces the overall weight of the bracket while maintaining structural rigidity and strength.
It is further desired to provide a bracket that reduces the possibility of the wedge getting jammed in an inserted position such that release is difficult to achieve.
It is still further desired to provide a bracket that may be universally mounted and utilized for both left-handed and right-handed drive trains.